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SubjectRe: [PATCH] USB-PD tcpm: bad warning+size, PPS adapters
On Sun, Dec 29, 2019 at 10:35:44PM -0500, Douglas Gilbert wrote:
> Augmented Power Delivery Objects (A)PDO_s are used by USB-C
> PD power adapters to advertize the voltages and currents
> they support. There can be up to 7 PDO_s but before PPS
> (programmable power supply) there were seldom more than 4
> or 5. Recently Samsung released an optional PPS 45 Watt power
> adapter (EP-TA485) that has 7 PDO_s. It is for the Galaxy 10+
> tablet and charges it quicker than the adapter supplied at
> purchase. The EP-TA485 causes an overzealous WARN_ON to soil
> the log plus it miscalculates the number of bytes to read.
>
> So this bug has been there for some time but goes
> undetected for the majority of USB-C PD power adapters on
> the market today that have 6 or less PDO_s. That may soon
> change as more USB-C PD adapters with PPS come to market.
>
> Tested on a EP-TA485 and an older Lenovo PN: SA10M13950
> USB-C 65 Watt adapter (without PPS and has 4 PDO_s) plus
> several other PD power adapters.
>
> Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>

Reviewed-by: Guenter Roeck <linux@roeck-us.net>

> ---
> drivers/usb/typec/tcpm/tcpci.c | 20 +++++++++++++++-----
> 1 file changed, 15 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/usb/typec/tcpm/tcpci.c b/drivers/usb/typec/tcpm/tcpci.c
> index c1f7073a56de..8b4ff9fff340 100644
> --- a/drivers/usb/typec/tcpm/tcpci.c
> +++ b/drivers/usb/typec/tcpm/tcpci.c
> @@ -432,20 +432,30 @@ irqreturn_t tcpci_irq(struct tcpci *tcpci)
>
> if (status & TCPC_ALERT_RX_STATUS) {
> struct pd_message msg;
> - unsigned int cnt;
> + unsigned int cnt, payload_cnt;
> u16 header;
>
> regmap_read(tcpci->regmap, TCPC_RX_BYTE_CNT, &cnt);
> + /*
> + * 'cnt' corresponds to READABLE_BYTE_COUNT in section 4.4.14
> + * of the TCPCI spec [Rev 2.0 Ver 1.0 October 2017] and is
> + * defined in table 4-36 as one greater than the number of
> + * bytes received. And that number includes the header. So:
> + */
> + if (cnt > 3)
> + payload_cnt = cnt - (1 + sizeof(msg.header));
> + else
> + payload_cnt = 0;
>
> tcpci_read16(tcpci, TCPC_RX_HDR, &header);
> msg.header = cpu_to_le16(header);
>
> - if (WARN_ON(cnt > sizeof(msg.payload)))
> - cnt = sizeof(msg.payload);
> + if (WARN_ON(payload_cnt > sizeof(msg.payload)))
> + payload_cnt = sizeof(msg.payload);
>
> - if (cnt > 0)
> + if (payload_cnt > 0)
> regmap_raw_read(tcpci->regmap, TCPC_RX_DATA,
> - &msg.payload, cnt);
> + &msg.payload, payload_cnt);
>
> /* Read complete, clear RX status alert bit */
> tcpci_write16(tcpci, TCPC_ALERT, TCPC_ALERT_RX_STATUS);
> --
> 2.24.1
>

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